US007576718B2
`
`(12) United States Patent
`Miyazawa
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 7,576,718 B2
`Aug. 18, 2009
`
`(54) DISPLAY APPARATUS AND METHOD OF
`DRIVING THE SAME
`
`(75) Inventor: Takao Miyazawa, Shimosuwa-machi
`(JP)
`(73) Assignee: Seiko Epson Corporation, Tokyo (JP)
`
`(*) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 742 days.
`(21) Appl. No.: 10/936,649
`(22) Filed:
`Sep. 9, 2004
`
`(65)
`
`Prior Publication Data
`US 2005/O116902 A1
`Jun. 2, 2005
`
`Foreign Application Priority Data
`(30)
`Nov. 28, 2003
`(JP)
`............................. 2003-399339
`
`(51) Int. Cl.
`(2006.01)
`G09G 3/30
`(52) U.S. Cl. ............................. 345/78:345/76; 345/77;
`345/80, 345/81: 345/82: 345/204
`(58) Field of Classification Search ................... 345/78,
`345/76-77, 80-82, 204
`See application file for complete search history.
`References Cited
`
`(56)
`
`U.S. PATENT DOCUMENTS
`6,476.784 B2 * 1 1/2002 Zavracky et al. .............. 345,88
`6,816, 144 B2 11/2004 Tsuchi ....................... 34.5/100
`6,989,826 B2
`1/2006 Kasai
`7.057,589 B2 * 6/2006 Shin et al. ..................... 345/82
`
`7.205,988 B2 * 4/2007 Nakamura et al. .......... 345/2O7
`2003/O122813 A1
`7/2003 Ishizuki et al.
`2004/0085086 A1* 5/2004 LeChevalier ................ 324,770
`2004/0227749 A1
`11/2004 Kimura
`2006.0114.192 A1
`6/2006 Kasai
`
`FOREIGN PATENT DOCUMENTS
`
`9, 2001
`2, 2003
`4/2003
`5, 2003
`T 2003
`T 2003
`9, 2004
`1, 2001
`
`EP
`1130 S65 A1
`JP
`A 2003-043993
`JP
`A 2003-114645
`JP
`A 2003-157.050
`JP
`A 2003-202837
`JP
`A 2003-216109
`JP
`A 2004-252419
`WO
`WO 01/006484
`* cited by examiner
`Primary Examiner Richard Hjerpe
`Assistant Examiner—Leonid Shapiro
`(74) Attorney, Agent, or Firm Oliff & Berridge, PLC
`
`ABSTRACT
`(57)
`To provide a technology for preventing effect of precharging
`from becoming nonuniform when the threshold Voltage of a
`driving transistor included in a current drive type pixel circuit
`is nonuniform. In the technology, before setting the internal
`state of each of current drive type pixel circuits, provided to
`corresponded to intersections of a plurality of data lines and a
`plurality of scanning lines, in accordance with light emission
`grayscales, precharge Voltages as Voltages to be applied to the
`data lines are specified. A predetermined current is Supplied
`to the current drive type pixel circuits via the data lines. A
`precharge Voltage is specified in accordance with Voltages
`appearing in the data lines after the predetermined current is
`Supplied.
`
`2 Claims, 14 Drawing Sheets
`
`DISPLAY
`MATRIX
`SECTION
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`PROGRAMMING CURREN
`SUPPLYING MEANS
`
`PRECHARGE
`VOLTAGE
`GENERATING MEANS
`
`
`
`VOLTAGE
`MEASURING MEANS
`
`
`
`CONTROLLING
`MEANS
`
`LG Display Co., Ltd.
`Exhibit 1018
`Page 001
`
`

`

`U.S. Patent
`
`Aug. 18, 2009
`
`Sheet 1 of 14
`
`US 7,576,718 B2
`
`300
`
`
`
`
`
`
`
`
`
`
`
`FIG. 1
`
`200
`
`DISPLAY MATRIX SECTION
`(DISPLAY REGION)
`
`DATA LINE DRIVER
`
`400
`
`CONTROL UNIT
`
`1OO
`
`LG Display Co., Ltd.
`Exhibit 1018
`Page 002
`
`

`

`U.S. Patent
`
`Aug. 18, 2009
`
`Sheet 2 of 14
`
`US 7,576,718 B2
`
`FIG. 2
`
`
`
`n
`l
`
`1.
`
`L
`Z
`-
`CD
`2
`2
`2.
`CC
`CD
`D
`
`LG Display Co., Ltd.
`Exhibit 1018
`Page 003
`
`

`

`U.S. Patent
`
`Aug. 18, 2009
`
`Sheet 3 of 14
`
`US 7,576,718 B2
`
`FIG. 3
`
`DISPLAY
`MATRIX
`SECTION
`
`
`
`
`
`PROGRAMMING CURREN
`SUPPLYING MEANS
`
`
`
`
`
`PRECHARGE
`WOLAGE
`GENERATING MEANS
`
`VOLTAGE
`MEASURING MEANS
`
`
`
`CONTROLLING
`MEANS
`
`LG Display Co., Ltd.
`Exhibit 1018
`Page 004
`
`

`

`U.S. Patent
`
`Aug. 18, 2009
`
`Sheet 4 of 14
`
`US 7,576,718 B2
`
`
`
`079 Lu? ES
`
`UUX
`
`LG Display Co., Ltd.
`Exhibit 1018
`Page 005
`
`

`

`U.S. Patent
`
`Aug. 18, 2009
`
`Sheet 5 of 14
`
`US 7,576,718 B2
`
`F.G. 5
`
`S1
`
`OPEN
`
`CLOSED
`
`OPEN
`
`S2 OPEN
`
`S3 OPEN
`
`VOLTAGE
`
`
`
`CLOSED
`
`OPEN
`
`F.G. 6
`
`in2
`in 1
`
`TIME
`
`Out3
`
`LOW
`
`HIGH
`
`LG Display Co., Ltd.
`Exhibit 1018
`Page 006
`
`

`

`U.S. Patent
`
`Aug. 18, 2009
`
`Sheet 6 of 14
`
`US 7,576,718 B2
`
`FIG. 7
`
`S1 OPEN
`
`CLOSED
`
`OPEN
`
`S2 OPEN
`
`costs
`
`OPEN
`
`S3 OPEN
`
`FIG. 8
`
`200
`
`41 Oe
`
`BSE
`SECTION
`
`
`
`
`
`
`
`TEMPERATURE
`DETECTING MEANS
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`PROGRAMMING CURRENT
`SUPPLYING MEANS
`
`PRECHARGE
`VOLTAGE
`GENERATING MEANS
`
`
`
`VOLTAGE
`MEASURING MEANS
`
`
`
`CONTROLLING
`MEANS
`
`LG Display Co., Ltd.
`Exhibit 1018
`Page 007
`
`

`

`U.S. Patent
`
`Aug. 18, 2009
`
`Sheet 7 of 14
`
`US 7,576,718 B2
`
`FIG. 9
`
`Vth
`
`T (TEMPERATURE)
`
`LG Display Co., Ltd.
`Exhibit 1018
`Page 008
`
`

`

`U.S. Patent
`
`Aug. 18, 2009
`
`Sheet 8 of 14
`
`US 7,576,718 B2
`
`F.G. 10
`
`
`
`as a
`
`an as a s
`
`- - -
`
`- - - - - - - - - - - - - -
`
`| | | | | | | | | | | { | -t | | | | | | | { } | | |
`COLUMN d
`COU
`COLUMN e
`
`DRIVER C
`
`LG Display Co., Ltd.
`Exhibit 1018
`Page 009
`
`

`

`U.S. Patent
`
`Aug. 18, 2009
`
`Sheet 9 of 14
`
`US 7,576,718 B2
`
`FIG 11
`
`
`
`
`
`
`
`
`
`DISPLAY MATRIX SECTION
`(DISPLAY REGION)
`
`
`
`CALIBRATION REGON
`
`DRIVERIC
`
`LG Display Co., Ltd.
`Exhibit 1018
`Page 010
`
`

`

`U.S. Patent
`
`Aug. 18, 2009
`
`Sheet 10 of 14
`
`US 7,576,718 B2
`
`F.G. 12
`
`
`
`PXEL
`CIRCUIT
`
`PXEL
`CIRCUI
`
`4.
`LL
`2
`1.
`?
`LU
`4.
`-
`CD
`4.
`Z
`2
`c
`O
`CMO
`
`-TION
`PXEL
`CIRCUIT
`
`LG Display Co., Ltd.
`Exhibit 1018
`Page 011
`
`

`

`U.S. Patent
`
`Aug. 18, 2009
`
`Sheet 11 of 14
`
`US 7,576,718 B2
`
`F.G. 13
`
`
`
`1.
`L
`2
`?
`l
`2
`-
`CD
`2
`2
`2
`ae
`C
`O
`
`130
`
`DATALINE DRIVER
`
`PRIOR ART
`
`LG Display Co., Ltd.
`Exhibit 1018
`Page 012
`
`

`

`U.S. Patent
`
`Aug. 18, 2009
`
`Sheet 12 of 14
`
`US 7,576,718 B2
`
`F.G. 14
`
`
`
`1 1 O
`
`a m. g. a
`
`p
`
`is as
`
`P
`
`a
`
`a di-
`
`is
`
`PRIOR ART
`
`LG Display Co., Ltd.
`Exhibit 1018
`Page 013
`
`

`

`U.S. Patent
`
`Aug. 18, 2009
`
`Sheet 13 of 14
`
`US 7,576,718 B2
`
`F.G. 15
`
`TC
`
`Tpr
`Te
`V - l- l
`V2- -
`
`PRIOR ART
`
`LG Display Co., Ltd.
`Exhibit 1018
`Page 014
`
`

`

`U.S. Patent
`
`Aug. 18, 2009
`
`Sheet 14 of 14
`
`US 7,576,718 B2
`
`
`
`
`
`(INBHHnO TWWII dO) \doA s dA
`
`
`
`
`
`
`
`(INEHH00 EÐHWT) \doA > dA|
`
`|
`
`| | |
`
`LG Display Co., Ltd.
`Exhibit 1018
`Page 015
`
`

`

`US 7,576,718 B2
`
`1.
`DISPLAY APPARATUS AND METHOD OF
`DRIVING THE SAME
`
`BACKGROUND OF THE INVENTION
`
`2
`transistor 211 and the gate of the second transistor 212 are
`commonly connected to the first Sub-Scanning line V1. The
`gate of the third transistor 213 is connected to the second
`Sub-Scanning line V2.
`The first and second transistors 211 and 212 are switching
`transistors used to accumulate charges in the storage capaci
`tor 230. The third transistor 213 is a switching transistor that
`is in an ON state during the light emission of the organic EL
`element 220. The fourth transistor 214 is a driving transistor
`that controls a value of current flowing in the organic EL
`element 220. The current value in the fourth transistor 214 is
`controlled by the amount of charges stored (i.e., accumulated)
`in the storage capacitor 230.
`FIG. 15 is a timing chart illustrating the normal operation
`of the pixel circuit 110. In FIG. 15, a voltage in the first
`Sub-Scanning line V1 (hereinafter, referred to as a first gate
`signal V1), a Voltage in the second Sub-Scanning line V2
`(hereinafter, referred to as a second gate signal V2), a current
`in the data line Xm (hereinafter, referred to as data signals
`Iout), and a current IEL in the organic EL element 220 are
`represented.
`A driving period Tc is divided into a programming period
`Tpr and a light emission period Tel. The driving period Tc is
`a period of time taken to update a light emission grayscale of
`each of the organic EL elements 220 within the display matrix
`section 120 one time. The driving period Tc is referred to as a
`frame period. A grayscale update is performed in a group of
`pixel circuits in a single row at one time and is sequentially
`performed in N groups of pixel circuits in the N rows during
`the driving period Tc. For example, when the grayscale
`update is performed on all of the pixel circuits 110 at 30 Hz,
`the driving period Tc is about 33 ms.
`The programming period Tpr is a period of time while the
`light emission grayscales of each organic EL element 220 is
`set in a corresponding pixel circuit 110. Here, programming
`indicates the operation of setting the light emission grayscale
`in the pixel circuit 110. For example, when the driving period
`Tc is about 33 ms and the total number N of the scanning lines
`Yn is 480, the programming period Tpr is less than about 69
`LS.
`During the programming period Tpr, the second gate signal
`V2 is set to a “low” level and the third transistor 213 remains
`turned off. Next, a current Im corresponding to the light
`emission grayscale flows in the data line Xm, the first gate
`signal V1 is set to a “high level, and the first and second
`transistors 211 and 212 are turned on. Here, the data line
`driver 140 functions as a constant current source that provides
`the current Im according to the light emission grayscale.
`Charges corresponding to the current Im flowing in the
`fourth transistor 214 (i.e., the driving transistor) are stored in
`the storage capacitor 230. As a result, a Voltage stored in the
`storage capacitor 230 is applied between the source and the
`gate of the fourth transistor 214. Hereinafter, the current Im of
`data signals used in the programming is referred to as a
`“programming current Im. After the programming is fin
`ished, the scanning line driver 130 sets the first gate signal V1
`to the “low” leveland turns off the first and second transistors
`211 and 212. The data line driver 140 stops outputting the data
`signals Iout.
`During the light emission period Tel, while the first gate
`signal V1 remains at the “low” level, the first and second
`transistors 211 and 212 remain turned off, the second gate
`signal V2 is set to the “high leveland the third transistor 213
`is turned on. Since the Voltage corresponding to the program
`ming current Im has been stored in the storage capacitor 230,
`almost the same current as the programming current Im flows
`in the fourth transistor 214. Therefore, almost the same cur
`
`1. Field of Invention
`The present invention relates to technology of setting the
`internal state of a current drive type pixel circuit correspond
`ing to light emission grayscales for the current drive type
`pixel circuit at a high speed.
`2. Description of Related Art
`In recent years, an electro-optical apparatus using an
`organic electroluminescent (EL) element has been progres
`sively developed. The organic EL element is a self-luminous
`element and does not require a backlight. Accordingly, a
`display apparatus using the organic EL element is expected to
`achieve low power consumption, a wide viewing angle, and a
`high contrast ratio. In this specification, the term "electro
`optical apparatus' means an apparatus that converts electrical
`signals into light. The electro-optical apparatus normally con
`verts electrical signals representing an image into light rep
`resenting the image and is particularly Suitable to implemen
`tation of a display apparatus.
`FIG. 13 is a block diagram of a conventional display appa
`ratus using an organic EL element. The conventional display
`apparatus includes a display matrix section (hereinafter,
`referred to as a “display region') 120, a scanning line driver
`130, and a data line driver 140. The display matrix section 120
`includes a plurality of pixel circuits 110 arranged in a matrix.
`Each pixel circuit 110 includes an organic EL element 220.
`Each of the pixel circuits 110 arranged in a matrix is con
`nected to one of a plurality of data lines Xm (where m=1,
`2. .
`.
`. . and M) extending in a column direction and is
`connected to one of a plurality of scanning lines Yin (where
`n=1,2,..., and N) extending in a row direction.
`FIG. 14 is a circuit diagram illustrating an example of the
`pixel circuit 110. The pixel circuit 110 is located at an inter
`section of an m-th data line Xm and an n-th scanning line Yn.
`The scanning line Yn includes two Sub-Scanning lines V1 and
`V2. The pixel circuit 110 is a current drive type circuit that
`controls a light emission grayscale of the organic EL element
`220 corresponding to a current flowing in the data line Xm. In
`detail, the pixel circuit 110 further includes four transistors
`211 to 214 and a storage capacitor 230 in addition to the
`organic EL element 220. The storage capacitor 230 stores
`charges corresponding to data signals received via the data
`line Xm to control the light emission of the organic EL ele
`ment 220 using the stored charges. In other words, the storage
`capacitor 230 stores a Voltage corresponding to the current
`flowing in the data line Xm. The first to third transistors 211
`to 213 are n-channel field effect transistor (FET) and the
`fourth transistor 214 is a p-channel FET. The organic EL
`element 220 is a current drive type light emission element like
`a photodiode and is thus marked with a symbol of a diode in
`the drawings.
`The source of the first transistor 211 is connected the drain
`of the second transistor 212, the drain of the third transistor
`213, and the drain of the fourth transistor 214. The drain of the
`first transistor 211 is connected to the gate of the fourth
`transistor 214. The storage capacitor 230 is connected
`between a source and the gate of the fourth transistor 214. The
`source of the fourth transistor 214 is connected to a power
`Supply Voltage Vdd.
`The source of the second transistor 212 is connected to the
`data line driver 140 via the data line Xm. The organic EL
`element 220 is connected between the source of the third
`transistor 213 and a ground Voltage. The gate of the first
`
`10
`
`15
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`LG Display Co., Ltd.
`Exhibit 1018
`Page 016
`
`

`

`US 7,576,718 B2
`
`5
`
`3
`rent as the programming current Im flows in the organic EL
`element 220. The organic EL element 220 emits light with a
`grayscale corresponding to the current value Im.
`In the display apparatus illustrated in FIG. 13, the light
`emission of the organic EL element 220 included in each
`pixel circuit 110 is controlled according to the above-de
`scribed sequence of operation. However, when a large display
`panel is manufactured using the above-described structure,
`the capacitance (Cd) of each data line increases and a large
`amount of time is required to drive the data lines. To solve
`these problems, “Patent Document 1 discloses technology
`for accelerating charge or discharge by writing the power
`supply voltage Vdd in the data line Xm connected to the pixel
`circuit 110 before programming a current corresponding to
`the light emission grayscale in the pixel circuit 110, that is,
`before setting an internal sate of the pixel circuit 110. Here
`inafter, the operation of programming a predetermined Volt
`age in a data line connected to a current drive type pixel circuit
`before the internal state of the pixel circuit is set correspond
`ing to the light emission grayscale of the pixel circuit, thereby
`accelerating the charge or discharge, which is referred to as
`“precharging”. A Voltage written in the data line by the pre
`charging is referred to as a “precharge Voltage'.
`Patent Document 1 Pamphlet of PCT Publication WO
`25
`01/006484
`
`4
`organic EL element 220 emits light with the low grayscale,
`since a current corresponding to the low grayscale is Small, it
`takes long to write a Voltage corresponding to the current in
`the storage capacitor 230, and therefore, the programming of
`the Voltage may not be satisfactorily performed during the
`programming period Tpr, which is referred to as “insufficient
`programming hereinafter.
`In view of the foregoing, it is an object of the present
`invention to provide a technology for preventing effect of
`precharging from becoming nonuniform when the threshold
`Voltage of a driving transistor included in a current drive type
`pixel circuit is nonuniform.
`To accomplish the above object, the present invention pro
`vides a display apparatus including a plurality of data lines; a
`plurality of Scanning lines; a plurality of current drive type
`pixels provided to corresponded to intersections of the plu
`rality of data lines and the plurality of scanning lines; Supply
`ing means which Supplies a predetermined current via the
`plurality of data lines to the corresponding pixels; and speci
`fying means which specifies precharge Voltages as Voltages to
`be applied to the data lines connected to the pixels before the
`internal state of the pixels corresponding to light emission
`grayscales is set, in accordance with Voltages appearing in the
`data lines after the Supplying means provides the predeter
`mined current.
`According to the display apparatus, the precharge Voltages
`are specified in accordance with the Voltages appearing in the
`data lines when the internal state of the pixels corresponding
`to the predetermined current is set. That is, the precharge
`Voltages are specified when the pixels are actually operated.
`Accordingly, if precharging is performed using the thus
`specified precharge voltages, a precharging effect is uniform
`even when the threshold voltage of a driving transistor
`included in each pixel is not uniform.
`In a more preferred aspect, the display apparatus may
`further comprises storage means which stores the precharge
`Voltages specified by the specifying means so as to corre
`spond to the pixels. In the aspect as described above, a pre
`charge Voltage specified for each pixel is stored in the storage
`means to corresponded to the pixel. Generally, in order to
`accurately specify an optimal precharge Voltage, a suffi
`ciently long time for programming is required and is usually
`longer than the time required to display an image. However,
`according to the present invention, for example, in factories
`before forwarding products, a precharge Voltage may be
`specified only one time and stored in the storage means.
`Accordingly, compared to a case where a precharge Voltage is
`specified wheneveran image is displayed, the time required to
`specify the precharge Voltage is reduced.
`In a more preferred aspect, the display apparatus may
`further comprises measuring means which measures the Volt
`ages appearing in the data lines after the Supplying means
`provides the predetermined current. The specifying means
`specifies the Voltages measured by the measuring means as
`the precharge Voltages. Since the specified precharge Voltages
`are the Voltages appearing in the data line when the pixels are
`actually driven, a precharging effect is uniform even when the
`threshold Voltage of a driving transistor included in a pixel is
`not uniform.
`In a more preferred aspect, the Supplying means Supplies
`the predetermined current to the pixels at least when electric
`power is applied to the display apparatus. Since the precharge
`Voltage for each pixel is specified when electric power is
`Supplied to the display apparatus, even when a driving tran
`sistor included in the pixel is degraded over time and has a
`threshold Voltage changed, the precharge Voltage is specified
`in accordance with the changed threshold Voltage.
`
`10
`
`15
`
`SUMMARY OF THE INVENTION
`
`When it is assumed that a driving transistor in each pixel
`circuit 110 operates in a saturation region, a current “Ids'
`flowing between a drain and the source of the driving transis
`tor (i.e., a current flowing in the organic EL element 220) is
`given by the following equation:
`Ids=(pre-Wp)/(2-tox-Lp)(Vgs-Vth),
`
`Expression 1
`
`30
`
`35
`
`where Vgs denotes a Voltage flowing between the gate and the
`source, Vth denotes a threshold voltage, Wp denotes a chan
`nel width, Lp denotes a channel length, up denotes a hole
`mobility, tox denotes the thickness of a gate insulation layer,
`and 6 denotes a dielectric constant of a gate insulation mate
`rial.
`When the threshold voltage Vth of the driving transistor is
`different from the pixel circuits 110, even though the organic
`EL elements 220 emit light with the same grayscale, a Voltage
`to be written in the storage capacitor 230 is different from the
`pixel circuits 110. When a voltage to be written in the storage
`capacitor 230 is different from the pixel circuits 110, an
`optimal precharge Voltage to be applied to a data line before
`the voltage is written in the storage capacitor 230 is also
`different from the pixel circuits 110. To solve this problem,
`the technology disclosed in Patent Document 1 always uses
`the power Supply Voltage Vdd as the precharge Voltage.
`Accordingly, a satisfactory effect by the precharging cannot
`be obtained in this technology disclosed in Patent document
`1. In detail, referring to FIG.16, when a precharge voltage Vp
`is much higher or lower than an optimal Voltage Vopt, a
`Voltage stored in the storage capacitor 230 (i.e., the gate
`Voltage of the driving transistor) is non-uniform even after the
`programming period Tpr lapses. When the gate Voltage of the
`driving transistor is not uniform, a current flowing in the
`organic EL element 220 becomes nonuniform and the light
`emission grayscale of each organic EL element 220 becomes
`nonuniform. In other words, the quality of a displayed image
`may deteriorate. The deterioration of the quality of a dis
`played image is particularly prominent when the organic EL
`element 220 emits light with a low grayscale. When the
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`LG Display Co., Ltd.
`Exhibit 1018
`Page 017
`
`

`

`5
`In a more preferred aspect, the predetermined current Sup
`plied to the pixels by the Supplying means corresponds to a
`current when the pixels are caused to emit light with a low
`grayscale. Generally, a programming current corresponding
`to the low grayscale becomes Small, resulting in an insuffi
`cient programming problem. However, if precharge Voltages
`are specified in accordance with to Voltages appearing in data
`lines when the internal state of pixels is set using the current
`corresponding to the low grayscale, the insufficient program
`ming problem can be avoided.
`In a more preferred aspect, the display apparatus may
`further comprises a display region in which the plurality of
`pixels is arranged in a matrix. The Supplying means Supplies
`the predetermined current to all the pixels arranged in the
`display region. The specifying means specifies the precharge
`voltages for all the pixels. In above-described aspect, the
`precharge Voltages for all the pixels arranged in the display
`region are specified through the actual operation of each
`pixel. Accordingly, a precharging effect is uniform even when
`the threshold voltage of a driving transistor included in the
`pixel is not uniform.
`In a more preferred aspect, the display apparatus may
`further include a display region in which the plurality of
`pixels is arranged in a matrix. The Supplying means Supplies
`the predetermined current to pixels belonging to a row
`selected from the display region. The specifying means speci
`fies the precharge Voltages for the corresponding pixels Sup
`plied with the predetermined current by the Supplying means
`and then specifies the average of the precharge Voltages as the
`precharge Voltage for the pixels in the selected row. In above
`described aspect, the precharge Voltages specified for the
`pixels belonging to the selected row are equalized in units of
`rows, and therefore, a calibration error is reduced.
`In a more preferred aspect, the display apparatus may
`further comprise a display region in which the plurality of
`pixels is arranged in a matrix. The Supplying means Supplies
`the predetermined current to pixels belonging to at least one
`row or column designated in advance in the display region.
`The specifying means specifies the precharge Voltages for the
`corresponding pixels Supplied with the predetermined current
`and then based on the distribution of the specified precharge
`Voltages, optimizes the precharge Voltages for the corre
`sponding pixels arranged in the display region. Here, the time
`required to specify the optimal precharge Voltages can be
`reduced compared to a case where precharge Voltages for all
`of the pixels are specified by actually driving all of the pixels
`in the display region. In addition, the storage capacity
`required for storing the specified precharge Voltages can be
`reduced.
`In a more preferred aspect, the display apparatus may
`further comprise a display region in which the plurality of
`pixels is arranged in a matrix. The Supplying means Supplies
`the predetermined current to calibration pixels disposed out
`side the display region along sides of the display region, and
`the specifying means specifies the precharge Voltages for the
`corresponding calibration pixels and then based on the distri
`bution of the specified precharge Voltages, optimizes the pre
`charge Voltages for the corresponding pixels arranged in the
`display region. In the above-described aspect, since the cali
`bration pixels are disposed outside the display region along
`sides of the display region, the specification of optimal pre
`charge Voltages and actual image display can be simulta
`neously performed without affecting the display quality of
`the display region.
`In a more preferred aspect, the calibration pixels may be
`dummy pixels that do not comprise any light emission ele
`ment. According to the above-described aspect, since the
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`US 7,576,718 B2
`
`10
`
`15
`
`6
`dummy pixels do not emit light when they are used to specify
`the precharge Voltages, the display quality of the display
`region is much less affected.
`In a more preferred aspect, the display apparatus may
`further comprise Switching means which selects either a first
`data line or a second data line for being connected to the
`Supplying means. The first data line is connected to the pixels
`arranged in the display region to display an image, and the
`second data line is connected to the calibration pixels. The
`calibration pixels are disposed such that the length of the
`second data line is smaller than that of the first data line.
`According to the above-described aspect, since the calibra
`tion pixels are connected to data lines other than the data lines
`connected to the pixels for image display, the floating capac
`ity of the data lines connected to the pixels for image display
`can be decreased, and therefore, the time required to specify
`a precharge Voltage can be reduced.
`In a more preferred aspect, the display apparatus may
`further comprise temperature detecting means which detects
`the temperature of the pixels, where the specifying means
`specifies the precharge Voltages based on the Voltages appear
`ing in the data lines and the temperature detected by the
`temperature detecting means. In the above-described aspect,
`even when the threshold voltage of a driving transistor
`included in a pixel changes due to an increase in the tempera
`ture of the driving transistor during image display, the pre
`charge Voltage can be specified in accordance with the
`changed threshold Voltage at that time.
`To solve the above object of the present invention, the
`present provides a method of driving a display apparatus. The
`method comprises the steps of a first step of Supplying a
`predetermined current to a plurality of current drive type
`pixels provided to corresponded to intersections of a plurality
`of data lines and a plurality of Scanning lines via the data
`lines; and a second step of specifying precharge Voltages as
`Voltages to be applied to the data lines connected to the pixels
`before the internal state of the pixels corresponding to light
`emission grayscales is set, in accordance with Voltages
`appearing in the data lines after the predetermined current is
`Supplied.
`According to the driving method, even when the threshold
`Voltage of a driving transistor included in the pixel is not
`uniform, a precharge Voltage for each pixel is specified when
`each pixel is actually driven. Accordingly, if precharging is
`performed using the thus specified precharge Voltage, a pre
`charging effect can be uniform.
`In a more preferred aspect, the first step may comprise
`Supplying the predetermined current to pixels belonging to at
`least one row or column designated in advance in a display
`region in which the plurality of pixels is arranged in a matrix.
`The second step may comprise specifying a plurality of the
`precharge Voltages for the corresponding pixels Supplied with
`the predetermined current, and then based on the distribution
`of the specified precharge Voltages, optimizing the precharge
`Voltages for the corresponding pixels arranged in the display
`region.
`Here, the time required to specify the optimal precharge
`Voltages can be reduced compared to a case where precharge
`voltages for all of the pixels are specified by actually driving
`all of the pixels in the display region. In addition, the storage
`capacity required for storing the specified precharge Voltages
`can be reduced.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a block diagram of a display apparatus according
`to the present invention.
`
`LG Display Co., Ltd.
`Exhibit 1018
`Page 018
`
`

`

`US 7,576,718 B2
`
`7
`FIG. 2 is a block diagram illustrating the internal structure
`of a display matrix section and the internal structure of a data
`line driver according to the present invention.
`FIG. 3 is a block diagram illustrating a fundamental struc
`ture of a single line driver 410 according to the present inven
`tion.
`FIG. 4 is a detailed block diagram of the single line driver
`410 according to the present invention.
`FIG. 5 is a timing chart illustrating the operation of the
`single line driver 410 according to the present invention.
`FIG. 6 illustrates the relationship between input and output
`signals of a comparator according to the present invention.
`FIG. 7 is a timing chart illustrating the operation) of the
`single line driver 410 according to the present invention.
`FIG. 8 illustrates a single line driver according to Modifi
`cation 1 of the present invention.
`FIG. 9 is a view illustrating an example of a temperature
`threshold Voltage characteristic of a driving transistor.
`FIG. 10 is a view illustrating a method of specifying a
`precharge Voltage according to Modification 2.
`FIG. 11 is a view illustrating a method of specifying a
`precharge Voltage according to Modification 3.
`FIG. 12 is a view illustrating a display apparatus according
`to the Modification 3.
`FIG. 13 is a block diagram of a conventional display appa
`ratus using an organic electroluminescent (EL) element.
`FIG. 14 is a circuit diagram illustrating an example of a
`pixel circuit 110 of a general display apparatus.
`FIG. 15 is a timing chart illustrating the normal operation
`of the pixel circuit 110 of the general display apparatus.
`FIG. 16 illustrates effects of different precharge voltages.
`
`DETAILED DESCRIPTION OF PREFERRED
`EMBODIMENTS
`
`5
`
`10
`
`15
`
`25
`
`30
`
`35
`
`8
`transistors (FETs). However, some or all of the transistors
`may be replaced with bipolar transistors or other types of
`Switching devices. For example, silicon-based transistors
`may be used as this kind of a transistor in addition to the thin
`film transistors (TFTs).
`The control unit 100 shown in FIG. 1 converts display data
`(i.e., image data) representing a display state of the display
`matrix section 200 into matrix data representing the light
`emission grayscale of each of organic electroluminescent
`(EL) elements 220. The matrix data includes scanning line
`driving signals sequentially selecting a single group of pixel
`circuits 110 in a single row and data line driving signals
`indicating the level of data signals supplied to the organic EL
`elements 220 in the selected group of the pixel circuits 110.
`The Scanning line driving signals are Supplied to the scanning
`line driver 300 and the data line driving signals are supplied to
`the data line driver 400. In addition, the control unit 100
`controls timing for driving the scanning lines Yin and the data
`lines Xm.
`The scanning line driver 300 selectively drives one of the
`plurality of Scanning lines Yn to select a group of pixel cir
`cuits 110 in a single row. The data line driver 400 includes a
`plurality of single line drivers 410 driving the respective data
`lines Xm. Each of the single line drivers 410 supplies data
`signals to a group of pixel circuits 110 in a row via a data line
`Xm. If the internal state of each of the pixel circuits 110 is
`programmed according to the data signals, a current flowing
`in each organic EL element 220 according to the programmed
`internal State is controlled. As a result, the light emission
`grayscale of the o